Processes for the preparation of α,α-branched carboxylic acids from branched olefins by means of a Koch synthesis, using carbon monoxide and water, are known. Thus, Koch, Gilfert and Huiskens developed in 1955 a two-stage operation (medium pressure synthesis where, in the first stage olefins react with an acid catalyst and carbon monoxide in the absence of water, followed by a second stage wherein the complex formed by the olefin, carbon monoxide and the acid catalyst is hydrolyzed. The reaction occurs at temperatures between 50 to 200° C. and pressures up to 100 bar. Generally H2S04, H3PO4, HF or Lewis acids such as BF3 are employed as catalyst. A review of Koch reactions, which review is included herein by reference, may be found in “New Synthesis with Carbon Monoxide”, edited by J.Falbe, ISBN 3-540-09674-4, © by Springer-Verlag Berlin Heidelberg 1980. Such technology is also described in U.S. Pat. No. 3,068,256 to Roming, included herein by reference, and in other patent literature.
From EP 1 033 360 a process is known for the synthesis of vinyl esters from butene oligomers, wherein butenes are oligomerized, the butene oligomers are separated from the oligomerized mixture, the butene oligomers are converted to carboxylic acids which are longer by one carbon atom, and the resulting carboxylic acids are converted to the corresponding vinyl esters. The butene oligomers are in particular dibutene, tributene and tetrabutene.
The vinyl esters are well known in the industry as monomer copolymerized with other unsaturated functional olefins that are used in coatings, adhesives and composite applications.
The carboxylic acids obtained by way of the Koch synthesis may be converted to the corresponding vinyl esters. This can be achieved, for example, by reacting the carboxylic acids with acetylene at normal pressure and 200 to 250° C., preferably in the presence of the zinc salt of the acid to be vinylated (for example, according to Encyl. Polym. Sci. Eng. 17, pp. 426-434, incorporated herein by reference). They may also be produced from the corresponding acid by reaction with ethylene and a copper catalyst.
Alternatively, the vinyl esters can be obtained by transesterification of the carboxylic acids with further vinyl esters such as vinyl acetate or vinyl propionate (as described, for example, in: Ullman, 4th Edition, Volume 19, pp. 368 ff., incorporated herein by reference. Industry may start from different sources of olefin oligomers to make the acid. Surprisingly, the inventors have found that the isomer distribution of an olefin oligomer mixture, and more specially the mixture based on a propylene trimer (so called PT3), has an important influence on the throughput of the synthesis of the vinyl ester. This relationship was not disclosed so far. On the other hand, it is obvious that a higher throughput is leading to economical and environmental benefits.
Surprisingly, the inventors have found a way to produce acid composition at a higher throughput in the vinylation step, as compared with the initial isomer composition.